Major Rivers and Lakes of Montana

Montana's Waterways: Headwaters of a Continent

Montana is a headwater state – its mountains feed three major drainage basins: Missouri-Mississippi (Gulf of Mexico), Columbia (Pacific), and Nelson (Hudson Bay).

Major Rivers (by Drainage Basin)

Missouri River Basin (Atlantic/Gulf)

• Missouri River: Forms at Three Forks (Jefferson + Madison + Gallatin). Longest US river.
• Yellowstone River: Longest undammed river in lower 48; joins Missouri in ND.
• Madison River: World-class trout; Hebgen & Ennis Lakes.
• Gallatin River: Yellowstone Park → Gallatin Canyon → Three Forks.
• Jefferson River: Beaverhead + Big Hole + Ruby → Three Forks.
• Clark Fork River: Butte → Missoula → Idaho → Pend Oreille → Columbia (Pacific).
• Bitterroot River: South→North, joins Clark Fork at Missoula.
• Blackfoot River: "A River Runs Through It"; joins Clark Fork near Bonner.
• Flathead River: Glacier Park → Flathead Lake → Clark Fork (Columbia basin).
• Kootenai River: BC → NW Montana → Idaho → Columbia.
• Mariás River: East of Rockies → Missouri.
• Milk River: Hi-Line → Missouri (Canada→US→Canada→US).

Hudson Bay Basin (Arctic)

• St. Mary River: Glacier Park → Alberta → Saskatchewan → Nelson → Hudson Bay.
• Belly River / Waterton River: Same basin.

Major Lakes & Reservoirs

Significance

• Headwaters for millions downstream.
• Blue-ribbon trout fisheries (Madison, Yellowstone, Bighorn, Missouri).
• Hydropower (Fort Peck, Hungry Horse, Kerr, Canyon Ferry).
• Irrigation (Milk River Project, Clark Fork, Bitterroot).
• Recreation economy (float, fish, paddle, ski).